1. Field of the Invention
The invention relates in general to a touch control apparatus and an associated selection method, and more particularly to an optical touch control apparatus and an associated selection method.
2. Description of the Related Art
Based on different operation principles, touch control technologies may be categorized into capacitive touch technology, resistive touch technology and optical touch technology. Among the touch control technologies, the optical touch technology calculates a position of a touch point through coordinates shielded by light, and can be easily applied to large-size applications while also having lower production costs.
FIG. 1A shows a schematic diagram of a conventional optical touch control apparatus determining a touch point of a single object. In short, in an optical touch control apparatus, after lights are emitted from light machines (M1 and M2), an image sensor detects whether a touch point (i.e. the object) exists to further determine coordinates of a position of the touch point.
The infrared light emitted from the light sources causes changes in a reflected light distribution at a position of the object. At this point, the image sensor, cooperating with a controller, may calculate the position of the touch point according to the changes in the reflected light distribution.
For illustration purposes, in the diagrams of the specification, an included angle formed by a connection line between the object O and the first light machine M1, and a fourth side IV of a display panel 14, is referred to as a left included angle θI. Similarly, an included angle formed by a connection line between the object O and the second light machine M2, and the fourth side IV of the display panel 14, is referred to as a right included angle θr. In the description below, it is assumed that sensors are disposed in the light machines, with M1 representing the first light machine/first sensor, and M2 representing the second light machine/second sensor.
In FIG. 1A, according to a triangle (L, R, IV) formed by the position of the object O and the two light machines (M1 and M2), the controller may obtain the upper-left angle and the upper-right angle (the left included angle θI and the right included angle θr) of the triangle. Coordinates of the touch point can then be calculated by a triangle function.
However, the conventional optical touch technology is inadequate in providing accurate touch points for multi-touch applications. When the number of the objects is plural, a conventional optical touch control apparatus may generate confusions when determining the touch points due to different combinations of multiple left included angles θI and right included angles θr.
In the description below, when a display panel generates multiple left included angles θI and multiple right included angles θr in the presence of multiple objects, numbers of the left included angles and the right included angles are defined in an increasing order of the included angles. For example, a smallest left included angle is numbered as θI1 , a smallest right included angle is numbered as θr1 , and so forth.
When there are multiple objects, a connection line L between the objects and the first light machine M1is represented according to the numbers of the left included angles. Similarly, a connection line R between the objects and the second light machine M2is also represented according to the numbers of the right included angles.
FIG. 1B shows a schematic diagram of a misjudgment on touch points by a conventional optical touch control apparatus when two objects exist on a display panel. In FIG. 1B, on a display panel 14, it is assumed that a position of a first object O1 is P1, and a position of a second object O2 is P2.
Therefore, according to a triangle formed by the first object O1, the first light machine M1 and the second light machine M2 , a second left included angle θI2 and a first right included angle θr1 can be obtained. Similarly, according to a triangle formed by the second object O2 , the first light machine M1 and the second light machine M2 , a first left included angle θI1 and a second right included angle θr2 can be obtained.
It can be concluded from the above, when two objects exist on the display panel 14, the sensors sense four included angles, i.e., the first left included angle θI1, the second left included angle θI2, the first right included angle θr1 and the second right included angle θr2.
When estimating touch points according to the first left included angle θI1 with the first right included angle θr1 and the second right included angle θr2, respectively, the controller obtains a candidate touch position F1 and a candidate touch position P2.
Further, when estimating touch points according to the second left included angle θI2 with the first right included angle θr1 and the second right included angle θr2 , respectively, the controller obtains a candidate touch position P1 and a candidate touch position F2.
That is to say, the four candidate positions (P1, P2, F1 and F2) can be derived from combinations of the four included angles. However, the candidate touch position F1 and the candidate touch position F2 are not actual positions of the touch points.
The controller determines the above candidate touch positions according to positions of shadows replied from the sensors. When selecting two out of four, two of the shadows are false, and are referred to ghost points. These ghost points lead the controller to misjudge the actual positions of the touch points, as in the example above. Thus, the candidate touch position F1 and the candidate touch position F2 in FIG. 1B are ghost points.
As previously stated, when there are two touch points, the first sensor obtains two left included angles, and the second sensor also obtains two right included angles. Combinations of the two left included angles and the two right included angles form four candidate touch positions. By deducting the actual positions of the touch points from the four candidate touch positions, there are two ghost points.
As the number of touch points increases, the number of shadows (the candidate touch positions) obtained by the sensors also becomes larger, meaning that possibilities of misjudging ghost points as touch points also get higher.
For example, with three objects (in equivalence to three touch points on the display panel), the first sensor senses to obtain three left included angles, and the second sensor also senses to obtain three right included angles. Combinations of the three left included angles and the three right included angles form nine candidate touch positions. After deducting actual positions of the touch points, there are as many as six ghost points.
It can be deduced that, the number of candidate touch positions is substantially equal to a square of the number of objects. Therefore, as the number of objects increases, when designing an optical touch control apparatus, there is a need for a solution for quickly eliminating positions of ghost points and to correctly select actual positions of touch points from numerous candidate touch positions.